Divide students into three groups.
Have one group do a conductor test.
Materials needed
a dry cell
bell wire
a flashlight bulb fitted into a miniature socket
Directions
Cut three pieces of wire each twelve inches long, strip the insulation on all ends about one inch. Attach one end of a wire to one terminal of the dry cell and the other end of the wire to one of the terminals to the socket. Attach one end of the second wire to the other terminal of the dry cell, then attach one end of the third wire to the other terminal of the socket. Take the ends of the free wires and touch them together to complete the circuit and the light should go on. Instead of touching the two ends of wire together touch them to the opposite ends of an iron nail, the bulb will light because the nail is a conductor. Try a piece of wood instead of a nail and answer the question as to whether the wood is a conductor. Any material can be tested this way to see whether or not it is a conductor.
Have the second group construct a switch.
Materials needed
a dry cell
a flashlight bulb in socket
three fifteen inch pieces of bell wire with stripped ends
rulers for measurement
a block of wood
a strip of metal
two nails
a hammer
Directions
Nail one end of the metal strip to the blocks of wood, letting the nail stick up a little, hammer the other nail, part of the way into the block of wood under the other end of the metal strip and bend the metal up so that it doesn’t touch the nail. Connect a wire from one terminal of the dry cell to one terminal of the socket. Connect the second wire from the other terminal of the dry cell to the nail that holds the metal strip. Connect the third wire to the other terminal of the socket and to the other nail. When the end of the metal strip is not touching the nail, the circuit is open and the bulb does not light. If the strip is pushed down to touch the nail, the circuit is closed and the bulb lights.
Have the third group do an electromagnet.
Materials needed
a dry cell
a switch
a large iron nail
four or five feet of bell wire
tacks
Directions
Strip the outer covering from the ends of the wire. Start about one third of the way along the wire, winding it tightly around the nail making as many turns as there is room for. After that, connect one end of the wire to a dry cell terminal and the other end to one of the nails in the switch. Take a short piece of wire, strip the ends and attach it to the other nail in the switch and the other terminal of the dry cell. Close the switch and the large nail with the current flowing in a coil of wire around it will become an electromagnet. Put some tacks underneath, the electromagnet will pick them up and hold them. When the switch is open the tacks will fall off.
Logic circuits
Objectives
To recognize a simple logic circuit
To use and or to find a true and false statements.
Circuits called logic gates control the flow of electricity either by blocking a signal or by letting it pass through.
Below are two kinds of circuit patterns. Electricity will light the light bulb if it can go from the power source to the bulb. If it cannot pass, the bulb will not light.
A closed switch lets an electric signal pass. 1 represents a closed switch.
An open switch blocks an electric signal. 0 represents an open switch.
(figure available in print form)
These two circuit patters are based on the following rules of logic.
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AND when and is used between
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OR when or is used between
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two statements, the whole
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two statements, the whole
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statement is true only
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statement is true whenever one
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when both statements are true.
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of the statements is true.
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5 + 2 = 7 and 6 + 3 = 17
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5 + 2 = 7 or 6 + 3 = 17
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is a false statement
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is a true statement.
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Provide data and have students construct a table.
The larger the resistance, the smaller the current. The greater the e.m.f. the greater the current.
Current is equal to e.m.f. divided by resistance. In mathematics it can be shown that 8 is divided 4 by writing 8/4. Ohm’s law can be shown the same way by writing
____
____
electromotive force (e.m.f.)
Let I stand for current; E for e.m.f.; and R for resistance and the formula is I = E/R. The formula can be changed to read E = IxR and R = E/I.
With Ohm’s law students can find out the amount of current, e.m.f. or resistance if they know the amount of any two of them.
Example:
If you have an e.m.f. of 8 volts, and a resistance of 4 ohms, how much current will flow? I = E/R.
I = 8/4 is 2 amperes
If they know that the current is 2 amperes and the resistance is 4 ohms, they can find the e.m.f. with the formula E = I x R or E = 4 x 2 and the answer is 8 volts.
The students can find the resistance if they know that the e.m.f. is 8 volts and the current is 2 amperes. R = E/I or K = 8/2. The resistance is 4 ohms.
Ohm’s law is the simple basis for most of all electrical calculations.
Provide data for classes and have them solve the problems.
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Have students bring in a copy of their parents electric bill and have them compute the bill based on kilowatt hours used.
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Invite speaker from power plant.
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Have speaker talk about electricity in general and specific terms.
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Plan a field trip to a local power plant.
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After field trip have students write a report on their experience.
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Have students write two word problems each. Divide the class into groups of twos and have them critique each others work.
